1. Field of the Invention
The present invention relates to impact printing devices and in particular to an improved print hammer for such devices and means for actuating the print hammer.
2. Description of the Prior Art
Plunger-type armature magnet systems are generally known in printing technology and have been successfully utilized as drive devices for the print hammer in type printing devices or for the printing needles in mosaic printing systems. Such a plunger-type armature magnet system for a type printing device is described, for example, in IBM Technical Disclosure Bulletin, Vol. 15, No. 8, January, 1973 at page 2356, and a drive circuit for print hammer systems is disclosed in IBM Technical Disclosure Bulletin, Vol. 19, No. 8, January, 1977 at pages 3107-3108.
The maximally attainable printing speed of impact printers employing plunger-type armature magnet systems for driving the print hammers of the printer is essentially governed by two factors. The first factor is the striking speed of the print hammer and the second factor is the amount of time necessary to return the print hammer of the magnet system to its initial rest position without significant rebounding oscillations after a character is printed.
The speed of movement of the armature in a plunger-type armature magnet systems essentially is controlled by the strength of the magnetic field generated by the excitation coil of the magnet system. When a plunger-type magnet system is employed as a drive device for the print hammer of a carriage moving line by line along a recording medium, the size and current handling capacity of the excitation coil are limited by the geometrical dimensions of the carriage which limit the cooling technology which can be utilized as well as limiting the weight of the magnet system.
The return velocity of the armature after completion of a printing stroke in a plunger-type armature magnet system, and thus the minimum time which must elapse until the magnet system can again be activated, greatly depends upon the damping to which the print hammer is subject at the recording medium. The degree of damping acting on the print hammer depends, among other factors, on the number of pieces of paper, that is, the number of copies, which are present at the printing station. A larger number of copies absorbs more kinetic energy from the print hammer during printing of a character and therefore subjects the print hammer to a greater amount of damping than a small number of copies.